The present invention relates to an exhaust muffling device for reducing exhaust noise by suppressing air column resonance.
Conventionally, in this type of exhaust muffling device installed in an internal combustion engine, a plurality of mufflers are arranged-over an exhaust pipe which communicates with an exhaust manifold in order to suppress air column resonance generated in the exhaust pipe. For example, a constitution is known whereby a length from a convergence point of an exhaust manifold to a terminal outlet of an exhaust pipe is set as a reference length (X), a first muffler is provided in a position of 3X/5 from the terminal outlet, and a second muffler is provided in a position of 2X/5 from the terminal outlet. This type of exhaust muffling device is disclosed in Japanese Laid-Open Patent Publication No. S59-226222.
By providing a plurality of mufflers in appropriate locations, this type of conventional exhaust muffling device is capable of muffling exhaust noise favorably. However, the overall weight is increased by the provision of the plurality of mufflers, which is likely to lead to an increase in cost. To consider this problem simply, if the second muffler of the exhaust muffling device described in Japanese Laid-Open Patent Publication No. S59-226222 were omitted, for example, then a pipe length from the first muffler to the terminal outlet would increase, and especially if this length were to reach or exceed 1.5 m, for example, air column resonance would occur in the normal rotation region of the internal combustion engine, causing the sound pressure level of the exhaust gas to increase.